Communication networks usually contain a multiplicity of terminals and a plurality of communication nodes. In circuit switched communication arrangements, for example in ISDN systems, each terminal in this arrangement is permanently registered with a respective communication node (switching center) and is thus permanently associated therewith. In this case, this association is provided by the cabling, so that a terminal, for example a telephone or a fax machine, is registered precisely with that switching center to which this terminal also has a physical connection.
The terminals in voice data networks, frequently also referred to as voice-over-IP networks (VoIP=Voice-over-Internet Protocol), are also permanently associated, and registered, with one of the communication nodes in the respective voice data network. By way of example, such voice data networks use the H.323 protocol (ITU-T-H.323) or the SIP protocol (SIP=Session Initiation Protocol) for signaling. In a voice data network—unlike in circuit switched communication networks—it is basically possible for any network component, that is to say any terminal and any communication node, to interchange data (particularly voice data) with any other network component directly. A fixed association among the network components, as provided in the circuit switched communication networks on the basis of the cabling, is neither imperative nor desirable in voice data networks. The terminals in voice data networks are frequently also referred to as “clients”, because these terminals differ significantly from circuit switched terminals. Thus, by way of example, they may be in the form of a telephone with a network connection or else in the form of a computer with a piece of communication software installed thereon. The communication nodes in the voice data networks are frequently also referred to as “gatekeepers” (H.323) or “proxies” or “SIP proxies” (SIP protocol), since the function of these communication nodes forms not only the connection initiation between the clients but also the access control for transfer devices to other networks, the “gateways”. In the text below, the term “gatekeeper” is used as standard for gatekeeper and (SIP) proxy, in order to simplify matters.
The communication nodes in the voice data networks store configuration data relating to those terminals which are registered with this communication node. These data are, by way of example, information about the authorizations of the respective client or of the user of the respective client, associations with call acceptance groups, the telephone number of the client etc. The communication node (gatekeeper) with which a client is registered is also referred to as the “home node” or “home gatekeeper”. If this client is now intended to be operated at a different communication node, then the corresponding terminal (client) is signed off from the home node and is registered with another communication node, also referred to as the “adoptive gatekeeper” if the change is only temporary. If, following registration, the configuration data stored at the home node are transferred to the “adoptive gatekeeper”, then the terminal can be operated at the adoptive gatekeeper in the same way as at its home node. If this “move” to the adoptive gatekeeper is not just brief (temporary), but rather permanent, then the adoptive gatekeeper now becomes the new home node for the terminal.
Such moves, like the one described above, by terminals from one communication node to another communication node are often prompted in order to ensure an even utilization level (“load balancing”) for the communication nodes in a communication network. Such a move may also be necessary “on an unscheduled basis”, for example if a terminal's home node fails or is no longer obtainable on account of a fault in the communication network. In that case, a substitute communication node, that is to say an adoptive gatekeeper, needs to adopt the function of the original home node either temporarily or permanently.
A drawback which has been found with the known communication networks is that the move by terminals from one communication node to another communication node needs to be controlled manually. Although computer aided tools are known for performing the necessary steps, for example transfer of the configuration data from one communication node to another communication node, automatically on the basis of a manual request, the decision regarding which terminal changes to which communication node at what time needs to be made manually and needs to be input into the system manually. In particular, when changing to the terminal in question or to the terminals in question, the network address of the “new” communication node needs to be added manually. Another drawback is that a merely temporary change of communication node, for example as a result of a fault, also requires the final restoration of the original state, that is to say the move by the terminal back to its original home node, to be initiated and performed manually.